I’m not sure I’ve ever seen advocates of gay rights — of equal rights, I should say — as revved up as they are right now, with the Supreme Court poised, today and Wednesday, to consider same-sex marriage in two separate cases.

But while they’re watching this moment raptly and hopefully, it’s not with a sense that the fate of the cause hangs in the balance. Quite the opposite. They’re watching it with an entirely warranted confidence, verging on certainty, that no matter how the justices rule, the final chapter of this story has been written. The question isn’t whether there will be a happy ending. The question is when.

In an astonishingly brief period of time, this country has experienced a seismic shift in opinion when it comes to gay and lesbian people. Look at the last month alone. Look merely at the Republican Party.

Although its 2012 platform called for a constitutional amendment to ban gay marriage, scores of prominent Republicans, including a few senior advisers to Mitt Romney’s campaign, broke ranks in late February and put their names to a Supreme Court amicus brief in favor of marriage equality.

That these dissidents can’t be dismissed as pure anomalies was made clear at the annual gathering of the recent Conservative Political Action Conference. CPAC, mind you, is no enclave of moderation and reason. It’s more like an aviary for the far-right “wacko birds” whom John McCain recently called out.

But as BuzzFeed’s Chris Geidner, who covered the conference, noted, “Opponents of gay rights spoke to a nearly empty room, while supporters had a standing-room-only crowd.”

Last week, in Politico, came the sweeping declaration that March 2013 would perhaps go down as “the month when the political balance on this issue shifted unmistakably from risky to safe.” That assessment reflected formal endorsements of same-sex marriage, in less than a week’s span, by both Rob Portman and Hillary Clinton.

Clinton, tellingly, didn’t just articulate her position in the course of a broader interview or speech. She released a precisely scripted video dedicated to marriage equality, and that spotlight and care spoke volumes about the way this issue has suddenly become central to Democratic politics.

What a difference four years make. In 2008, both Clinton and Barack Obama publicly opposed same-sex marriage. Just a year ago, that was still Obama’s formal stance. But by the summer of 2012, marriage equality had made its way into the party platform. Now it’s woven into the party’s very fiber.

There’s no going back. In a recent ABC News/Washington Post survey, respondents nationwide favored marriage equality by a 58-36 margin. That’s an exact flip of a similar survey just seven years ago. And among young Americans, who will obviously make up more and more of the electorate as time goes by, support was stronger still: 81 percent of people in the 18-29 age group in the survey endorsed marriage equality.

The buildup to the Supreme Court hearings has demonstrated the breadth of diversity of support for it. There have been amicus briefs signed, or proclamations of solidarity issued, by dozens of professional athletes and by the American Academy of Pediatrics, by tech giants and accounting firms and retailers and airlines.

The advances have happened in largest part because of the increased visibility of gay people who have had the courage and optimism to share their lives and truths with family, friends, colleagues.

Although many critics nitpicked Portman for changing his views only out of what was deemed a selfish concern for his own gay son, that’s precisely the way many people are illuminated and tugged along.

The decades-long rallying cry of the gay-rights movement — come out, come out, so that Americans understand the impact of discrimination on people they care about — was predicated on that wrinkle of human nature.

Additionally, the quest for same-sex marriage has forced many Americans to view gays and lesbians in a fresh light. We’re no longer so easily stereotyped and dismissed as rebels atop parade floats, demanding permission to behave outside society’s norms. We’re aspirants to tradition, communicating shared values and asserting a fundamentally conservative desire, at least among many of us, for families, stability, commitment.

And who really loses if we win? Where’s the injured party? The abortion debate grinds on in part because to those who believe that life begins at conception, every prochoice victory claims victims.

The gun debate grinds on because new restrictions are just that — restrictions. But the legalization of same-sex marriage takes nothing from anyone, other than the illusion, which is all it ever was, that healthy, nurturing relationships are reserved for people of opposite sexes.

The Supreme Court cases and their resolutions do matter. If the court doesn’t dismantle the Defense of Marriage Act, there’s no telling how many more years will pass before gay and lesbian couples married in states that allow such weddings are treated equally under federal law. And the court could, in its ruling on the constitutionality of a California ban against same-sex marriage, hasten the spread of marriage equality beyond those nine states and the District of Columbia.

But fairness is where we’re heading, at least in regard to marriage, which has emerged as the terrain on which Americans are hashing out their feelings about gays and lesbians.

The trajectory is undeniable. The trend line is clear. And the choice before the justices is whether to be handmaidens to history, or whether to sit it out.

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Frank Bruni’s column is distributed by the New York Times News Service.